PROJECT SUMMARY Emerging and re-emerging infections are now widely acknowledged to be an urgent and growing global threat to human health. Nowhere is this more important than in urban slums, where humans are typically crowded, often inherently vulnerable, and live in close proximity with animal and environmental reservoirs of infection. Leptospirosis, a zoonotic disease caused by a spirochetal agent transmitted by rats, has emerged as an important health problem as slum settlements have expanded rapidly worldwide. In countries such as Brazil, large epidemics occur each year in slum communities during seasonal periods of heavy rainfall. These outbreaks are associated with life-threatening manifestations such as pulmonary haemorrhage syndrome (LPHS), for which case fatality is >50%. The burden of leptospirosiswili continue to increase as the world's slum population doubles to two billion by 2025. We therefore need to address critical gaps in our understanding of the transmission dynamics of leptospirosis such that novel and informed strategies for prevention can be identified and effectively implemented in slum communities.